Different types of light emitters have different performance characteristics that are more or less useful in different circumstances or when used in different ways. The various light-emitting technologies have different characteristics, advantages, and disadvantages. For example, liquid crystals are simple to control and have a highly developed and sophisticated technological infrastructure. Organic light-emitting diodes (organic LEDs) are area emitters, can be more efficient and flexible, and are demonstrated in a very thin form factor. Inorganic light-emitting diodes are very efficient and provide relatively saturated light in an environmentally robust structure. Lasers are also efficient, provide a virtually monochromatic light, but have a limited viewing angle. None of these technologies, however, meet all of a display viewer's needs under all circumstances.
The relative benefits of different kinds of inorganic LEDs can vary depending on the color of the light emitted, the use of the LEDs, and the ambient conditions. For example, LED efficiency, lifetime, and cost varies depending on the LED brightness, size, and color. Furthermore, the human visual system is more sensitive to some colors, for example green, and less sensitive to others, for example blue.
The relative benefits of ILEDS and OLEDs also vary based on the color of the light emitted by the light-emitting device. Micro-transfer-printed inorganic LEDs are bright (e.g., having intensities from 300 W/cm2 to 500 W/cm2) and enable low power consumption. However, for example, green ILEDs suffer from the “green gap”, a portion of the light spectrum where the efficiency of green LEDs plummets.
OLEDs are thin, light, flexible, and consume less power than LCD displays. Additionally, OLEDs are easier to produce than the liquid crystals used in LCD displays. However, blue OLEDs have shorter lifetimes and are less efficient than red and green OLEDs. Similarly, red OLEDs have relatively longer lifetimes but are less efficient than green OLEDs. Moreover, the manufacturing process for dense arrays of OLEDs is relatively difficult and expensive. Furthermore, metal screens (fine metal masks) are used during the OLED manufacturing process to pattern the emitting materials deposited as layers onto the display substrate. These metal screens, also known as shadow masks, include rectangular openings (or apertures) for material deposition. A display (e.g., a 1024 by 768 display) can include almost eight hundred thousand pixels. Thus, openings in the mask must be created very precisely. This adds considerable expense to the OLED manufacturing process.
There is a need, therefore, for display structures with improved characteristics and manufacturing processes.